@pixel: just write \thechapter. in the \titleformat definition. Similar for sections.
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Stefan Kottwitz♦Feb 5 '11 at 14:23

Ok. It worked. I've also did same in report.cls to add dot in ToC.
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pixelFeb 5 '11 at 19:34

@pixel: Generally it's not a good idea to directly modify a class file, though it's a quick fix for now. I recommend to use \renewcommand within your document instead to redefine the respective macro. Other documents might base on report.cls, so you would change their layout as well, also your future report documents.
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Stefan Kottwitz♦Feb 5 '11 at 19:41